Unsaturated rubbers are vulcanized using not only sulfur, but also vulcanization accelerators. These are selected depending upon the intended application and desired characteristics of the rubber. Groups of accelerators, which have differentiated properties within each group, are, for example, thittram disulfides, dithiocarbamates, benzothiazolesulfen-amides, N-arylguanidines, some amines, polyamrines, thioureas and derivatives of dialkylthiophosphoric acids, such as O,O-dialkyldithio-phospliate metal salts.
The complex salt prepared from N,N'-diphenylguanidine, boric acid and pyrocatechol (DBB) is one specific accelerator compound. This comiipouiid has only moderate acceleration action. ##STR1##
The added accelerators undergo change on vulcanization. In many cases, secondary amines are formed, which form nitrosamines with nitrosamine-foirmers from the environment (for example, atmospheric NO.sub.x, nitrite in the solids). Nitrosamines are considered carcinogenic, such that the formation thereof during rubber vulcanization is unwanted.